The present invention relates to synchronous micromotors. The invention relates in particular to a self-starting synchronous micromotor comprising two-stage coils, permanent magnets serving as a rotor, a circular cylindrical stator with elongated portions which have such a configuration as to make the magnetic flux of the AC magnetic field developed by said coils effectively intersect the magnetic flux existing on the cylindrical circumferential surfaces of said permanent magnets, a closed AC magnetic circuit with minimum magnetic loss and no gap formed in the AC magnetic circuit and a third magnetic circuit.
Many types of induction synchronous motors have been proposed heretofore. While motors of this type have a self-starting capability, they are free to start rotation in either direction. It is thus essential with such motors to provide some mechanical control to assure rotation in the desired direction. Such mechanical structure often results in failure of starting of the motor and increases the possibility of faulty operation of the motor due to wear and other problems encountered with such mechanical structure.
In addition, with previously known induction motors it is essential to use a rotor which has a relatively large moment of inertia as well as a relatively large weight in order to achieve smooth rotation. This relatively large moment of inertia and weight of conventional motors of the above type reduces considerably the self-starting capability of the conventional motors. Thus, it is known that a micromotor having a rotor of relatively large weight and increased moment of inertia is largely influenced by the starting power and operation power so as to achieve only a low operation efficiency while generating undesirable heat.
Furthermore, with conventional motors of the above type N and S poles are developed between the stator and rotor. As a result permanent magnets cannot be used effectively.